This research project will build on the foundation which our present efforts provide to develop a sound understanding of the mechanistic features of the photodegradation of selected polyhaloarenes of environmental health significance. This knowledge will be of benefit in understanding how potentially harmful haloarenes are transformed or created photochemically in the environment and in the development of new methods for toxic waste disposal. Efforts will be focused on (1) the determination of the role of direct fission of singlet and triplet state species and that of excimers and exciplexes as product-determining intermediates, (2) the analysis of the mechanistic basis of the regiochemistry, the use of electron transfer reagents that absorb in the sunlight range in the photodehalogenation of haloarenes that do not absorb in the sunlight range, and (3) the phototransformations of polyhaloarenes in micellar systems with and without additional electron transfer reagents. In addition, attention will be devoted to the photochemical transformations of polyhaloarenes on nonreactive surfaces, in particular, the photochemical degradation of polychlorodibenzodioxins and polychlorodibenzofurans, the analyses of the nature of the fragmentation of radical anions through use of a trochoidal electron monochromator/MS system, and the application of the mechanistic conclusions to the design and testing of small-scale reactors for toxic waste disposal.